1. Field of the Invention
The present invention relates to a resist additive which improves hydrophobicity of the surface of a resist film to prevent materials from being leached from the resist film in water during an immersion lithography process and is converted to have hydrophilicity by deprotection reaction during a development process, and a resist composition including the resist additive.
2. Description of the Related Art
With higher integration and higher speed of large scale integrated circuits (LSI) in recent years, accurate micropatterning of photoresist is required. As exposure light sources used in the formation of resist patterns, a g-line (436 nm) or i-line (365 nm) from a mercury lamp has been widely used.
However, as resolution improvement obtained by adjusting exposure wavelength approaches physical limits, a method of using shorter wavelength was introduced as a finer patterning technology of a photoresist. For example, a KrF excimer laser (248 nm), an ArF excimer laser, or the like having a shorter wavelength than i-line (365 nm) is being used.
In ArF immersion lithography using an ArF excimer laser as a light source, the space between a projection lens and a wafer substrate is filled with water. According to this method, a pattern may be formed using a refractive index of water at 193 nm even when a lens having an NA of 1.0 or greater is used, and this method is commonly referred to as immersion lithography. However, since a resist film directly contacts water, acids generated by a photoacid generator or amine compounds contained in the resist film as a quencher may be easily dissolved in water. Thus, the resist pattern may be deformed or may collapse due to swelling, or various defects such as bubbles and watermarks may be generated.
Accordingly, a method of forming a protective film or an upper film between the resist film and water to prevent the resist film from coming in contact with a medium such as water has been introduced. Such resist protective films need to be formed on a resist film while having sufficient light transmittance at the exposure wavelength so as not to interrupt exposure without being intermixed with the resist film, need to have and maintain stability without being leached by a medium such as water during liquid immersion lithography, and need to be easily dissolved in an alkali solution that is a developer during development.